Which metal is protected by a layer of its own oxide?

Aluminum forms a thin layer of its own oxide on its surface when reacts with atmospheric oxygen.

$4\mathrm{Al}+3{\mathrm{O}}_2\to 2{\mathrm{Al}}_2{\mathrm{O}}_3$

This layer acts as a protective barrier on the surface of the metal, which increases its durability, protects the aluminum from reacting with other metals, and increases its resistance against corrosion.